This invention relates to cable ties and more particularly to self-locking cable ties molded from a stretch-oriented plastic material.
Heretofore cable ties have been molded to the dimensions of the end product. In order for such ties to meet tensile strength requirements, the strap portions of such ties had a relatively large cross-sectional area. This large area was required because the molecules of the molded thermoplastic material were relatively unoriented and, accordingly, the material lacked the strength of material which was stretch-oriented. Additionally, difficulties were encountered in molding ties having a long strap portion because increased heat and pressure were required to completely fill the mold cavity. The increased heat may tend to cause degradation of the thermoplastic material while the increased pressure could cause the mold to pump open (flash). Examples of prior art molded cable ties are shown in U.S. Pat. Nos. 3,186,047 and 3,660,869.
Straps of stretched thermoplastic material have been proposed for bundling packages or a plurality of objects and for attaching tags and buttons to clothing. Examples of such straps are shown in U.S. Pat. Nos. 3,444,597 and 3,447,207. Such prior art straps have usually not been self-locking and required separate crimp connectors for application to an overlapped portion of the strap.
One self-locking stretched strap has been proposed which includes an elongate strap portion having a plurality of transverse rungs and a head portion having an integral locking pawl which is biased to a position between consecutive rungs. Of course, it has only locking positions corresponding to the rungs. As it is not infinitely adjustable, in certain applications it only provides a loose bundle or an overly tight bundle. Such a ladder construction also requires a long head to ensure there is a rung to engage the pawl upon cutoff of the strap tail flush with the head. A long head is also needed because sufficient space is required between consecutive rungs to allow pawl movement therebetween. Of course, longitudinal stretching of such a strap causes only the sides to increase in tensile strength because the rungs are not stretched significantly. Since the rungs do not contribute to the tensile strength of the material, such a structure results in an inefficient use of material. Also, this type of strap does not provide a uniform pressure on the bundle because of the alternate rungs and apertures and because the sides are harder than the rungs. Nonuniform pressure on the bundle could cause an undesirable stress concentration on the bundled wires. Reference may be made to U.S. Pat. No. 3,766,608.